1. The Field of the Invention
The present invention is in the field of joint repair surgery, such as reconstruction of the anterior cruciate ligament (ACL). More particularly, the invention relates to tensioning devices for applying loads to soft tissue grafts used in joint repair procedures.
2. The Relevant Technology
Injuries to joints, specifically the knee, are quite common, particularly when one engages in vigorous sporting activities. A common injury is a rupture or tear of the anterior cruciate ligament (“ACL”), which is the primary ligament responsible for holding the knee joint together and which keeps it from slipping out of joint or dislocating. An unrepaired ruptured or torn ACL can cripple, and would most certainly limit physical activity of, the person suffering a ruptured or torn ACL. Absent reconstruction of the ACL, such injuries would likely be the end of professional sports careers and would prevent ordinary people from enjoying an active life involving sports and like recreation.
Improvements in surgical procedures have made ACL reconstruction procedures more successful and more common. In general, an ACL reconstruction procedure involves taking a soft tissue graft from another part of the body, such as the patellar tendon or the hamstrings, and attaching it at both ends through a hole drilled through the two bones that make up the knee joint: the femur and the tibia. When secured in place, the soft tissue graft will mimic and take the place of the ACL itself. This soft tissue graft holds the femur and tibia together to make the joint more stable, but is flexible enough to allow for normal joint movements (i.e., flexion and extension).
Graft tension in ACL reconstruction has been recognized as an important factor in the clinical outcome of the ACL reconstruction procedure. Grafts that are too loose may be unstable, and grafts that are too tight may greatly restrict motion of the knee. Recent interest in graft tension and scientific work on the subject have raised the demand for quality instruments that will assist the surgeon in more effectively fixing ligament grafts under known tension.
Publications in the past few years have emphasized the need for adequate tensioning of the graft. These include Markolf et al., “Biomechanical Consequences of Replacement of the Anterior Cruciate Ligament With a Patellar Ligament Allograft. Part Two: Forces in the Graft Compared with Forces in the Intact Ligament,” J. Bone Joint Surg. Am., 78:11, 1728–34 (November 1996); Tohyama et al., “Significance of Graft Tension in Anterior Cruciate Ligament Reconstruction. Basic background and clinical outcome,” Knee Surg. Sports Traumatol. Arthroscopy, 6 Suppl. 1, S30-7 (1998); Andersen et al., “Review on Tension in the Natural and Reconstructed Anterior Cruciate Ligament,” Knee Surg. Sports Traumatol. Arthroscopy, 2:4, 192–202 (1994); Yasuda et al., “Effects of Initial Graft Tension on Clinical Outcome After Anterior Cruciate Ligament Reconstruction. Autogenous Doubled Hamstring Tendons Connected in Series of Polyester Tapes,” Am. J. Sports Med., 25:1, 99–106 (January 1997). For purpose of disclosure, the foregoing publications are incorporated herein by specific reference.
While much of the focus has been directed to the issue of under tensioning, which typically results in knees that are less stable than normal, application of too much tension may in theory also have an adverse effect by constraining the joints or causing increased pressure on articular surfaces.
A recent study by Hamner et al. has added to the understanding of graft tension by demonstrating that unequal tension in the individual strands of the soft tissue graft can result in significant losses in total graft strength and stiffness. Hamner et al., “Hamstring Tendon Grafts for Reconstruction of the Anterior Cruciate Ligament: Biomechanical Evaluation of the Use of Multiple Strands and Tensioning Techniques,” J. Bone Joint Surg. Am., 81:4, 549–57 (April 1999). Hamner et al. studied whether tensioning the soft tissue strands by hand would result in equalization of the load borne by each strand. Hamner et al. showed that this method was not effective in equalizing the load on the strands, which led to an ultimate graft strength that was not significantly greater than the strength of the individual strands taken alone.
Previous work has been done to develop and patent devices that are used to apply a known tension to cruciate ligament grafts. Such devices have typically included simple spring scales that apply a known load to the graft as a whole. E.g., U.S. Pat. No. 4,712,542; U.S. Pat. No. 5,037,426; U.S. Pat. No. Re 34,762; U.S. Pat. No. 5,713,897; U.S. Pat. No. 5,507,750; and U.S. Pat. No. 5,562,668. For purposes of disclosing mechanisms for applying a known load or tension onto a soft tissue graft, the foregoing patents are incorporated herein by specific reference.
Because none of the foregoing references disclose any method for using these devices to separately tension multiple soft tissue grafts so as to equalize the stress applied to each, one strand will often be preferentially loaded more than another, thus resulting in disparately conditioned and pre-tensioned strands that are not significantly stronger or stiffer than a single strand. More particularly, because hamstrings can have different diameters, simply applying a standard load to both strands simultaneously could result in one graft being subjected to a different material stress than the other graft. Moreover, even in the case of hamstrings or other soft tissue grafts that have the same or substantially the same diameters, inadvertent or unavoidable error by the treating surgeon, such as unequal conditioning of each soft tissue graft, can still lead to uneven loads being borne by each individual graft. Regardless of the causes for unequal application of material stress to each of the individual soft tissue grafts, the “tighter” graft (or graft with higher material stress) will reach the failure point first, thereby causing a lower load to failure for the composite graft.
In view of the foregoing, it would be an improvement in the art of joint repair to provide apparatus and methods for independently conditioning and pre-tensioning individual soft tissue graft strands, such as a pair of hamstrings used in an ACL reconstruction procedure.
It would be an additional improvement in the art to provide apparatus and methods for conditioning and pre-tensioning individual graft strands so that each graft strand could substantially contribute to the overall strength and stability of the repaired joint.